Improvement in refining bullion



UN T STATES n'rnnr men.

FREDERICK H. BQUSFIELD, OF SAN FRANCISCO, CALIFORNIA.

IMPROVEMENT IN REFINING BULLION.

Specification forming part of Letters Patent'No. 150,675, dated May 12,1874; application filed March 11, 1874.

To all whom it may concern:

Be it known that I, FREDERICK H. Bons- FIELD, of San Francisco city andcounty, State of California,have invented a Process for BeneficiatingBaseMetal Bullion; and I do hereby declare the following descriptionsufficient to enable any person skilled in the art or science to whichit most nearly appertains to make and use my said invention withoutfurther invention or experiment.

It is a well-known fact that in working the ore from the Comstock ledgeby pan process, much of the contained precious metals escapes a firstamalgamation, as slimes, tailin gs, &c., and that the working of theseform a distinct and separate branch of the metallurgical industry of theState of Nevada.

In the process of this extraction much sulphate of copper is used,which, by the combined action of the mineralized silver, the iron of thepan, and the quicksilver used, becomes partly or wholly reduced to themetallic state, and is with the precious metals amalgamated.

The resulting bullion comes under the de-- nomination of base, and mayrange between g and fine, according to the quantity of sulphate used,and its subsequent perfect or imperfect reduction and amalgamation. Thisclass of bullion is also produced in working copperized silver ores bythe various processes now in use for silver extraction, and it is to thebeneficiating of such that my process applies.

The disadvantageswhich this bullion suffers under, and which is theobject of this process to remove, are numerous, among which may bementioned, first, in its crude state, as it comes from theretorting-house, it is unnecessarily bulky and heavy, enforcing a largeextra consumption of time and fuel to run into bars; second, asbars--when the alloy is below fine no reliance can be placed upon assaystaken in the European fashion of chipping a corner, thus necessitatingthe expense of remelting the whole mass of metal in order to obtain afair assay sample to determine the value critically; third, the cost ofcarriage of this bullion from the mines to the market center, and fromsuch to Europe, where this bullion is generally refined, is considerablyaugmented, the charges embracing both value and weight; fourth, thediscount which bankers are obliged to impose on this class of bullion toprotect themselves against contingencies of all kinds, and whichdiscount is, for the most part, a clear loss to the producer of bullion.

I claim to be able to remove by my process from sixty to eighty percent. of contained baseness, thus removing the above objectionablefeatures, and to be able to utilize, at small expense the baseness soremoved.

The process consists in subjecting, in suitable vessels, to the combinedaction of a mixture of nitric acid of a certain specific gravity andweak sulphuric acid, the crude bullion as it comes from the retort, orthe metal in a granulated state. The chemical reaction which immediatelysets in, even in the cold, but which is also greatly promoted by heat,is as follows: The nitric acid of the mixture is decomposed by thecopper of the alloy, furnishing nitric-oxide gas, which is volatile andthree equivalents of oxygen. These three equivalents of liberated oxygenhaving an affinity for the copper, at once convert that metal .intooxide, which is at once dissolved and held in combination in the weaksulphuric acid.

When the action is sufficiently advanced the liquid may be decanted andevaporated to a certain density, when sulphate of copper willcrystallize out, and the granulations of silver, which are not dissolvedunless an excess of nitric acid is used,washed, and melted intocomparatively fine bars.

In the ordinary process of refining this bullion, all the metals,excepting gold, are oxidized at the expense of the sulphuric acid, whichis decomposed into the required amount of oxygen, and an equivalentamount'of sulphurous acid. The metals, with the above exception, go intosolution, and thesilver 1s recovered by precipitating with metalliccoper. 7 p The oxidation in my process takes place without the lossofany portion of the sulphuric acid, the necessary oxygen beingsupplied, as before explained, by the nitric acid.

Should any of the silver go into solution through mistake in adding morethan the calculated amount of nitric acid, it may be recovered withoutcompromising any of the previously-explained advantages, by adding tothe solution a sufficiency of the suboxide of copper.

Having thus described my invention, what I claim, and desire to secureby Letters Patcut, is-

The process of using the combined acids as a means of effecting theoxidation of the base metal without interfering with the integrity ofthe fine metals.

In witness whereof I hereunto set my hand and seal.

FREDERICK HENRY BOUSFIELD. [L. s] Witnesses:

J. L. Rooms, 0. M. RIoHAnDsoN.

